In the present description, “data” means textual information, which includes one or several symbols or characters, audiovisual information, synchronisation information, positioning information or other information. The data transmitted in the data signals is defined by one or several very short pulse sequences whose coding can be defined by the time difference between each pulse.
Ultra-wide band data transmission technology is achieved using data signals that include a series of very short pulses without using a carrier frequency. The width of these pulses can be less than 1 ns. Since the data signal pulses are very short in the time domain, when converting into the frequency domain, this leads to an ultra-wide band spectrum, which defines UWB technology. The frequency spectrum can range from 500 MHz to several GHz. The frequency bandwidth is generally greater than 25% of the central frequency for ultra-wide band technology.
Data transmission via ultra-wide band technology applies normally to a short distance with low transmitted pulse power. This is generally due to the fact that the frequency spectrum is shared with narrow band transmission devices. This means that a single pulse is generally received with a lower power level than the noise level. Thus, it is often necessary to combine the energy from more than one pulse to transmit a single symbol or character in order for it to be recognised by the receiver device.
For the transmission of coded data signals, which includes one or more successive sequences of N very short pulses, the pulses can be of different shapes provided that their width is generally less than 1 ns. They may be, for example, Gaussian shape pulses with one or two polarities or alternations.
Since several ultra-wide band (UWB) transmitter and receiver devices can be located in spatial proximity while transmitting data signals, as a rule, the transmitted data signal sequence coding is unique for the transmitter device. In this way, the receiver device can recognise the coded signals from a particular transmitter device. Furthermore, all of the codes used for coding data are, as a rule, orthogonal, which means that when they are mutually correlated, the correlation results in a value close to 0.
Usually, the data transmitted in pulse sequence signals can be coded for example by pulse position modulation (PPM). The time difference between two consecutive pulses and the instant when the first pulse of each sequence appears can thus define the desired coding for the data communication. In order to do this, the pulses of each sequence are transmitted at a pulse repetition frequency (PRF), which can be greater than for example 10 MHz. Each of the pulses is thus transmitted in a repetition window of a determined length, which can be for example 20 ns or more. As a function of the desired time coding, the pulse may be in advance or in retard compared to a determined theoretical transmission position so as to be able to code for example a “0” or a “1”.
When a pulse sequence coded signal transmission is carried out as above-mentioned, it is necessary that the pulses can be detected as a function of their position determined by the PPM during the signal reception in the receiver device. This generally requires a high time coherence in transmitter and receiver devices for the detection of transmitted data.
The coded data signals, which are transmitted by the transmitter device, can be reflected or refracted by various obstacles before being captured by the receiver device. Consequently, several time shifted coded signals, i.e. direct and/or multiple path signals, which include identical data, can be captured by the receiver device.
Several techniques for demodulating the information contained in coded data signals received by a conventional receiver device have already been proposed in the past. One of these known techniques consists in correlating coded data signals captured and shaped in the receiver device with an early replica and a late replica of the reference signal. The correlated early and late signals are then integrated, and a code adjustment is made for each replica in a code control loop until the level of the integrated early and late signals is identical. However, if all of the multiple path signals have to be detected, several correlation stages are used in parallel. Consequently, the electric power consumption of the receiver device is large, and many electronic components are necessary for processing signals in the receiver device, which constitutes a major drawback.
US Patent Application No. 2003/0095609 discloses a UWB method and apparatus for receiving several time spaced signals. The ultra-wide band signals are received by an antenna of the apparatus in order to be correlated in a correlator with a replica generated via a precision time generator. In order to obtain a replica like the coding of the signals captured by the antenna, the generator is clocked by a clock signal of a time base, and receives a code control signal from a code source. At the correlator output, the intermediate signals undergo temporal integration prior to demodulation and summation of the pulses in order to retrieve the information from the received ultra-wide band signals.
One drawback of this apparatus is that a correlation operation has to be carried out prior to demodulating and adding the pulses of the intermediate signals to retrieve the information. Moreover, the shape of the pulses must be known, and only the direct path signals or one of the multiple path signals can be detected with this apparatus, which is a drawback.
U.S. Pat. No. 6,483,461 discloses an ultra-wide band signal reception apparatus, which includes the same elements as the apparatus in US Patent Application No. 2003/0095609 so as to be used for positioning purposes. Consequently, the same drawbacks are noted as with the reception apparatus of the preceding Patent Application.
US Patent Application No. 2003/0058963 discloses a method and a device for receiving ultra-wide band type pulse signals. The signals include a heading frame for synchronisation retrieval in the reception device. In order to do this, the ultra-wide band signals are received by an antenna of the device and first of all compared to a threshold voltage in a comparator. At the output of the comparator, intermediate signals represent the sign of the received signal with respect to a threshold voltage. These intermediate signals are then sampled in sampling means, and sliding correlation is performed on a final set of samples using a reference replica to remove noise. This set of sample results of an addition of several groups of sampled signal samples. Each group of samples represents one of the pulses of the ultra-wide band signals. The temporal width of each group is equal to or greater than the reverse of a pulse repetition frequency of the ultra-wide band signals.
One drawback of such a device is that the information relative to the sign of pulses of ultra-wide band signals has to be exclusively used. Furthermore, the synchronisation verification has to be carried out by using information after the correlation operation. A pulse energy maximisation in the set of sample from the addition directly is not carried out, which is another drawback.
US Patent Application No. 2003/0198308 discloses a UWB time reference delay-hopped TR/DH communication system. The system reception device includes several pulse pair correlators operating in parallel to perform auto-correlation of the signals received by an antenna, and an analogue-digital converter at the output of each correlator. The information is subsequently demodulated using a known CDMA technique.
One drawback of this device is that it is necessary to carry out correlation operations as soon as the UWB signals are received, which complicates the realisation of this device in the same way as for US Patent Application No. 2003/0095609. Further, the communication system is limited to double pulse signals.
US Patent Application No. 2003/0002347 discloses an ultra-wide band signal reception apparatus, which includes the same elements as the apparatus of US Patent Application No. 2003/0198308 so as to be used for positioning purposes. Consequently, the same drawbacks are observed as with the reception apparatus of the preceding Patent Application.
It is thus a main object of the invention to overcome the drawbacks of the prior art by providing a wireless data communication method via ultra-wide band coded data signals that is able to process simply all of the direct path and/or multiple path coded signals captured by the receiver device.
It is another object of the invention to provide a wireless data communication method via coded ultra-wide band data signals for maximising the amplitude of the data pulses in relation to the noise captured by the receiver device.